There are a great many underground pipelines in use today and many more are predicted for installation in the future. When a pipeline is laid in a trench or ditch, whether it be an initial installation of the pipeline, or a reinstallation of the pipeline after recoating or other treatment, the trench must be filled in about the pipeline. Naturally, the operator must be careful not to drop large boulders or rocks on the pipeline when filling the trench for fear of damaging the pipeline. It is therefore common to initially cover the pipeline, to a depth of perhaps a foot, with padding material, which is normally just the finer materials removed when the trench was dug. After a padding layer is in place about the pipeline, larger rocks and boulders can then be used to fill the trench without fear of damaging the pipeline.
In excavating a trench, it is common to build up the material removed from the trench in a spoils bank on one or both sides (sometimes called the right of way) of the trench which runs the length of the trench. Normally, the spoils bank will be a homogeneous mix of finer materials, intermediate materials, and larger materials like boulders or rocks.
Over the years, a number of devices have been developed for segregating the spoils by size and dumping the finer materials into the trench to pad the pipe, with the remaining materials sometimes added subsequently to fill in the trench. U.S. Pat. No. 3,701,422 issued to Downey on Oct. 31, 1972, illustrates a modified road grader which is capable of segregating materials by size and conveying the finer materials over the ditch to pad the pipeline. U.S. Pat. No. 4,633,602 issued to Layh, et al. on Jan. 6, 1987, discloses a method and apparatus for padding pipe. This patent discloses a machine which is self-propelled along the spoils bank which segregates material by size and delivers the finer materials to the pipeline for padding while discharging the coarser materials behind the machine. U.S. Pat. No. 4,955,754 to Klamar issued on Sep. 11, 1990, discloses yet another pipeline padding system. In this system, the segregating device is suspended over the pipeline and moved along the pipeline. The device segregates the material, dropping the finer materials on the pipeline first, and then sequentially dropping medium size and larger size materials in the trench thereafter.
Despite the efforts in the technology to perform the padding operation with greater efficiency and economy, a need still exists for a padding machine which is more effective, less expensive and reliable in operation.